@@toStringTag property attributes + general semantics

[caitp]

Editorial note
Should define whether @@toStringTag is writable, enumerable and configurable. All @@toStringTag properties in the ES6 spec are non-writable and non-enumerable, and configurable.

I think we really need to define these. Matching the values on the builtin properties is probably good, because fewer inconsistencies between DOM & JS is good.

The other issue with these properties, is making InterfacePrototype.@@toStringTag === "InterfacePrototype" while Interface.@@toStringTag === "Interface" --- I don't believe we want to give Interface an instance property @@toStringTag, so the alternative is making @@toStringTag a getter which returns a distinct value depending on the receiver --- but this kind of sucks?

So yeah, I don't think we have a good answer for these semantics right now. It's probably worth discussing it a bit

[bzbarsky]

The interface vs interface prototype issue is covered by https://www.w3.org/Bugs/Public/show_bug.cgi?id=28244

[caitp]

I guess we'll try Erik's idea and see if it breaks anything

[caitp]

Tangentially related to this thread:

@bzbarsky given what you're saying in https://lists.w3.org/Archives/Public/public-script-coord/2015JulSep/0022.html --- Maybe Window (or just WindowProxy, but I don't think that works well for Blink atm) needs an [Unforgeable] readonly toStringTag/isConcatSpreadable, with a primitive value.

Does that seem sensible, or too restrictive on same-origin objects?

[bzbarsky]

I don't see why we need anything unforgeable on Window at all. You do need something on cross-origin WindowProxy instances, of course.

I think making same-origin access not do the right thing here would be quite confusing to consumers....

[annevk]

This got fixed in #357.